Many projection systems and other imaging devices incorporate high intensity arc-light sources that have small point sources that are called “fireballs.” The fireball is usually located within a concave reflector that has a focal point, such as a parabolic, elliptical, or other curved shaped mirror. The light emanating from the fireball in the focal point is reflected off the surface of reflector. Often times the reflector is made of a glass, metal, or other substrate that requires a special coating to be applied to provide a specular surface for reflection. When the reflector is fabricated, the special coating may be deposited, sprayed, dipped, painted, or otherwise applied to the reflector surface. The quality of the special coating may need to be determined to ensure that the special coating was applied properly. For instance, the amount of reflection at various wavelengths may need to be determined. Further, the consistency of the reflective surface may need to be examined over a substantial portion of the special coating.
Prior inspection techniques used a fiber source at the focal point of the reflector. The fiber source was oriented to allow light escaping it to scan across the surface of the reflector while with difficulty maintaining the fiber's spatial position at the focal point. Another problem with using an optical fiber included not being able to control the angular spread of the emerging light beam which causes the spatial extent (area) of the scanned region on the reflector surface to vary based on the relative tilt of the fiber.
Accordingly, a more flexible and efficient method of testing the reflective coating is needed to lower the cost and increase the quality of reflectors used for arc light sources. Having a better method of testing will ensure rapid alignment and accurate testing of reflector surfaces.